DE10314991A1 - Process for increasing the molecular weight of a polymer granulate - Google Patents

Abstract

The invention relates to a method for increasing the molecular weight of a polymer granulate from a polycondenstion system. Said polymer granulate is at least partially crystallised and is brought into direct contact with nitrogen-containing treatment gas which is guided in a circuit in a post condensation stage . The temperature of the polymer granulate in the post condensation stage is increased to between 175 250 DEG C with respect to the granulate from the polymer condensation system. A nitrogen rich unburnt gas which is obtained from air by means of physical methods and which has a residual oxygen content of between 0.1 5 vol. % and which also contains hydrocarbons is added to the treatment gas before it is directed via an oxidation stage and subsequently, to the post condensation stage.

Description

The The invention relates to a method for increasing the molecular weight of a Polymer granules that come from a polycondensation plant, at least is partially crystallized and in a post-condensation a circulated nitrogen-containing treatment gas is brought into direct contact, wherein the temperature of the polymer granules in the post-condensation compared to granulate coming from the polycondensation plant is increased to 175 to 250 ° C. The treatment gas ensures the equalization of the after-condensation Temperature and the removal of those formed by chemical reactions By-products.

As Polymer come polyester, for example polyethylene terephthalate (PETP), Polybutylene terephthalate (PBTP), polypropylene terephthalate (PTTP) or copolyesters and polyamides (PA) in question. These polymers will pure or doped, preferably for the production of packaging materials, such as films and bottles or e.g. B. for the production of high viscosity Yarns and fibers used.

The polycondensation of various monomers and the increase in molecular weight by post-condensation is known. Details are, for example, in EP 0 685 502 B1 , in Römpp, "Chemie-Lexikon", 10th edition, p. 1316, and in Houben-Weyl, "Methods of Organic Chemistry", 4th edition, volume E20, part 1, "Solid-phase polycondensation (post-reaction in solid phase ) ".

polycondensation are described in Ullmann's "Encyclopedia of Technical Chemistry", 4th edition, volume 19, pages 117-119.

Out DE 100 43 277 a method is known in which nitrogen and possibly hydrocarbon-containing exhaust gas from the polycondensation system is mixed with the treatment gas in a volume ratio of 1: 1 to 1: 1000 before it is passed into the post-condensation. The hydrocarbons are removed in an oxidation stage upstream of the post-condensation, additional oxygen being added if necessary. With this method, the addition of pure, oxygen-free nitrogen from the outside in order to compensate for leaks can be reduced or eliminated altogether.

However, this method can only be used if the post-condensation system is in close proximity to the polycondensation system in order to enable the supply of its hydrocarbon-containing exhaust gas. Another disadvantage is that the process control in the post-condensation system depends on the operating state of the polycondensation system. Malfunctions in the polycondensation plants therefore also lead to malfunctions in the downstream post-condensation plant. The retrofitting of existing plant complexes with a process according to DE 100 43 277 becomes complex and in some cases is even economically nonsensical.

For generation Different methods are used for nitrogen from air. Usually used to obtain technically pure nitrogen the pressure swing absorption process using molecular sieves. The "Linde" process of air liquefaction with following Fractionation is preferred when high purity nitrogen and at the same time the noble gases contained in the air are extracted should. In addition, nitrogen can also be removed from air using membrane separation processes getting produced. It is also known that from technical nitrogen the oxygen can be removed by giving it flammable gases such as Hydrogen, ammonia or the like are added and the gas mixture is catalytically oxidized.

All Methods are described, for example, in "Ullmann's Encyclopedia of Industrial Chemistry", Sixth Edition.

The The invention is based, the polycondensation process mentioned above continue to improve and at the same time an inexpensive and at the same time reliable solution to find.

This is achieved according to the invention by admixing the treatment gas with a nitrogen-rich fresh gas obtained from the air by means of physical or chemical methods and having a residual oxygen content of 0.1 and 5.0% by volume, preferably 1.0 to 3.0% by volume, of oxygen and hydrocarbons before that Treatment gas is passed through an oxidation stage and then into the post-condensation.

The Nitrogen-rich fresh gas can be obtained from air at low cost, for example through the above-mentioned pressure swing absorption processes are generated.

The nitrogen-rich fresh gas and the hydrocarbons can used treatment gas premixed or added separately become.

For use in the post-condensation, the treatment gas may max. 100 ppm oxygen contain. Therefore, the Amount of hydrocarbons mixed into the treatment gas is sufficient to be in the oxidation state by the nitrogen-rich fresh gas supplied Residual oxygen if possible Completely to remove.

The Hydrocarbons should be selected are from the group of alkanes, alkenes and alkynes or mixtures from these. Propane, butane, petroleum ether, LPG or are preferred their mixtures used. As LPG this is used to heat Apartments in use LPG designated.

The The amount of hydrocarbons added is determined based on the measurement the carbon monoxide content, the hydrocarbon content, the oxygen content or the so-called "lambda value" (the ratio Oxygen content to hydrocarbon content) of the treatment gas regulated according to the oxidation level. The regulation based on is preferred the measurement of the carbon monoxide content, since this measurement has no residual oxygen in the treatment gas required. Methods and devices for making these measurements are known to the person skilled in the art.

The treatment gas then passed into the post-condensation is practical free of oxygen and is expediently dried before it enters the post-condensation.

design options the procedure will be explained with the help of the drawing. she shows one possible Flow diagram of the method without the invention on this design option to limit.

From a polycondensation plant known per se ( 1 ) you get polymer granules, which you in the line ( 2 ) leads to crystallization to avoid sticking. This crystallization can be carried out in one or more stages. Methods for this are known to the person skilled in the art. A two-stage crystallization is described below.

In the first stage ( 3 ) the polymer granules in the fluidized bed are removed from the line by means of nitrogen-rich fluidizing gas ( 4 ) fluidized and brought to an elevated temperature. The temperature in the fluidized bed is in the range from 100 to 250 ° C. and preferably at least 150 ° C. The polymer granulate then passes through the line ( 5 ) to the second crystallization stage ( 6 ), which is designed, for example, as a paddle mixer, where the granules are heated indirectly.

The two-stage crystallization, usually with an increase in temperature in each stage, already ensures an increase in the degree of crystallization, but not a sufficient increase in the molecular weight of the polymer. To further increase the molecular weight and thus also the viscosity, the post-condensation reactor ( 8th ) to which the granules are fed through the line ( 7 ) feeds. The reactor ( 8th ) is led through the line ( 9a ) dry, practically oxygen-free treatment gas, the main component of which is nitrogen. The treatment gas is passed upwards through the fixed bed in the reactor, the temperature being made more uniform and reaction products removed. The residence times of the granules in the reactor ( 8th ) are usually in the range of 8 to 22 hours. Polymer granules with increased molecular weight are withdrawn from the reactor ( 8th ) on the line ( 10 ) and it expediently leads to cooling and dedusting, not shown.

Used treatment gas is extracted from the post-condensation reactor ( 8th ) on the line ( 11 ) withdrawn and with the gas of the line ( 12 ) mixed. The gas mixture formed is led through the line ( 13 ) for dust removal by a cyclone ( 14 ) and dedusted gas is passed through the line ( 15 ) with the help of the blower ( 16 ) suctioned off and onto the lines ( 17 ) and ( 18 ) distributed. The gas of the pipe ( 17 ) passes through the heater ( 19 ) and the management ( 4 ) back to the first crystallization stage ( 3 ).

The gas flow of the line ( 18 ) after fine cleaning as treatment gas in the reactor ( 8th ) recycled. First you give the gas the pipe ( 18 ) by the management ( 30a ) Hydrocarbons too.

Through the line 30b the nitrogen-rich gas obtained from air using physical methods is mixed in to compensate for gas losses. The order of addition can also be reversed. It is also possible to 30a ) admix the nitrogen-rich gas and the hydrocarbons together, if necessary after prior mixing.

Initial heating takes place in the indirect heat exchanger ( 20 ). Then you put the gas through the pipe ( 21 ) a heater ( 22 ) to on the line ( 22a ) the desired inlet temperature for the oxidation reactor ( 23 ) to reach. The oxidation reactor ( 23 ) contains, for example, a fixed bed of a granular oxidation catalyst (for example based on platinum or palladium) in order to oxidatively remove hydrocarbons. If necessary, oxygen is passed through the line (e.g. in the form of air) 24 ) fed.

That the reactor ( 23 ) by the. Management ( 25 ) leaving gas has an elevated temperature which can be close to 400 ° C. The gas gives some of its sensible heat in the heat exchanger ( 20 ) and then flows through the line ( 26 ) to another heat exchanger ( 27 ) before it goes through the line ( 28 ) drying ( 29 ) is supplied. The drying can, for example, work in an absorbent manner known per se. The dried gas flows through the line ( 9 ) to the heat exchanger ( 27 ) and gets through the line ( 9a ) as treatment gas in the reactor ( 8th ). This treatment gas preferably has a carbon monoxide content of 10 to 500 mg / Nm ³ .

It is also possible that additional nitrogen-containing exhaust gas from the polycondensation plant is mixed with the treatment gas in a volume ratio of 1: 1 to 1: 1000 before it is passed to the post-condensation. A method for admixing nitrogen-containing exhaust gas from the polycondensation plant to the treatment gas has ended DE 100 43 277 known. In this case, the nitrogenous exhaust gas is led in front of the fan ( 30 ) in the line ( 18 ) on.

In a conventional polycondensation plant ( 1 ) is produced from terephthalic acid, isophthalic acid and ethylene glycol polyethylene terephthalate (PETP), which is further processed according to the drawing. The change in the polycondensation state of the PETP granules is shown in Table I: Table I

It is used with a fluidized bed crystallizer ( 3 ) at 160 ° C and a paddle crystallizer ( 6 ) worked at 205 ° C, the residence time in the fluidized bed crystallizer is 15 minutes and in the paddle crystallizer 60 Minutes. In the reactor ( 8th ) the granulate is in the fixed bed. At a temperature of 205 ° C the residence time in the reactor is ( 8th ) 11 hours. An electric heater ( 22 ) and absorption drying ( 29 ) used with a molecular sieve. The fluidized bed crystallizer ( 3 ) 7532 kg / h PETP granules of 60 ° C are fed in through the line ( 24 ) air is brought in. Gas quantities and temperatures are shown in Table II: Table II

Gas compositions are given in Table III, where OK means organic components: Table III

Claims (7)

Process for increasing the molecular weight of a polymer granulate which comes from a polycondensation plant, is at least partially crystallized and is brought into direct contact in a post-condensation with a nitrogen-containing treatment gas, the temperature of the polymer granules in the post-condensation compared to the granules coming from the polycondensation plant to 175 to 250 ° C is increased, characterized in that a nitrogen-rich fresh gas with a residual oxygen content of 0.1-5% by volume and hydrocarbons obtained from the air by means of physical methods is mixed with the treatment gas before it is passed through an oxidation stage and then into the post-condensation. A method according to claim 1, characterized in that the amount of hydrocarbons added is sufficient to remove the oxygen in the oxidation state, which is caused by the nitrogen-rich fresh gas obtained from air was supplied. A method according to claim 1 or 2, characterized in that that the hydrocarbons are selected from the group of Alkanes, alkenes and alkynes or their mixtures. A method according to claim 3, characterized in that the hydrocarbons are selected from the group containing propane, butane, LPG or mixtures thereof. A method according to claim 1 to 4, characterized in that that the amount of hydrocarbons blended based on the measurement the carbon monoxide content, the hydrocarbon content, the oxygen content or the relationship Oxygen content to hydrocarbon content of the treatment gas the oxidation level is regulated. A method according to claim 1 to 5, characterized in that one in addition nitrogen-containing exhaust gas from the polycondensation plant to the treatment gas in volume ratio from 1: 1 to 1: 1000 admixed before it is sent to the post-condensation becomes. Process for producing a nitrogen-rich gas for use in increasing the molecular weight of a polymer granulate that comes from a polycondensation plant, in which at least in a reactor containing nitrogen-containing inert gas is introduced, at least partially crystallized and the polymer granules are brought into direct contact with a nitrogen-containing treatment gas in a post-condensation, the temperature of the polymer granules in the post-condensation being increased to 175 to 250 ° C. compared to the granules coming from the polycondensation plant , characterized in that nitrogen gas-rich fresh gas with a residual oxygen content of 0.1-5% by volume and hydrocarbons are added to the treatment gas by means of physical methods before it is passed through an oxidation stage and then into the post-condensation.